If your trailer has electric brakes it has a little 5x5x3" plastic box around the tounge usually. Inside there is a battery to actuate the brakes. The truck just sends a signal to the trailer and the trailer battery pwrs the brakes. The battery needs to be charged once in awhile. I've found once in the spring and again in aug works for us.Posted via Mobile Device

How you can tell yours is charging is plug it in, start the truck, and with a multi meter set for 12v, check the battery and it should show 13v-14v. At rest, the battery will only show between 12v-13v.

If it's not charging, check to see that the lead out of the trucks plug for "12v" is hot when it's running. If it is, then maybe your trailer is not setup for that wire to charge the battery??